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First pictures advice

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#1 Keudn

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Posted 14 September 2018 - 01:15 PM

Hi guys, I got my first EQ mount yesterday and I excitedly mounted my DSLR to it and took it outside to play around. I ended up saving some subs of Andromeda, and after processing them in PI I have noticed I have some issues with the stars. They appear to me to be out of focus, even though I double checked that I had good focus with BYN. Can someone with more experience help me figure out what is causing my star issues and how to fix it? I know for sure that my mount was not polar aligned very well, but I wasn't noticing any star trailing for the 30s subs that I was doing at 200mm. Is this coma and I need to stop down my lens?

 

Camera - Nikon D5300

Lens - Nikon DX AF-S NIKKOR 55-200mm f/4-5.6G ED

Mount - Meade LXD75 EQ

 

Processing

20x30s Lights

30x30s Darks

118 Bias

17 Flats

 

Processed in PixInsight 1.8

 

Image in question


Edited by Keudn, 14 September 2018 - 01:15 PM.


#2 Adun

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Posted 14 September 2018 - 01:42 PM

I don't have more experience, but I know that is not star trailing.



#3 Richoff

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Posted 14 September 2018 - 02:00 PM

 I had the same thing (Sony rig), went back the next night and made 100% sure I had sharp focus, and also stopped down my 300mm f4 lens down to f8... that took care of the problem for me.

Regards



#4 Mike7Mak

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Posted 14 September 2018 - 02:02 PM

Definitely focus, and something else like field curvature or rotation from poor polar alignment. No experience with camera lenses so that's all I got.


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#5 fewayne

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Posted 14 September 2018 - 02:13 PM

+1 to Mike7Mak. The little donuts are diagnostic. That looks far enough off that you should be able to do better by just switching to Live View and magnifying. No criticism intended, just an avenue of investigation for you. You could note the position you obtain with your best visual effort, take a frame, focus using BYN, take a frame, and compare the results. You could also try making a Bahtinov mask and comparing the results with that to BYN's.

 

Again, no offense: Did you remember to turn off autofocus?



#6 fender2547886

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Posted 14 September 2018 - 02:16 PM

can you be certain that the zoom in not dragging? Can you post one sub rather than a stacked image?

dj



#7 Keudn

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Posted 14 September 2018 - 02:41 PM

+1 to Mike7Mak. The little donuts are diagnostic. That looks far enough off that you should be able to do better by just switching to Live View and magnifying. No criticism intended, just an avenue of investigation for you. You could note the position you obtain with your best visual effort, take a frame, focus using BYN, take a frame, and compare the results. You could also try making a Bahtinov mask and comparing the results with that to BYN's.

 

Again, no offense: Did you remember to turn off autofocus?

Yeah I had autofocus off, and I had focused it in BYN. The best I was able to do in the frame and focus window was ~3.1 (whatever units those are). I did have some fog on the camera lens, I wiped it off but I was unable to get the lens completely clear, maybe I had something smudging it. Either way wiping the lens off didn't seem to change anything in my previews. Plus the 3.1 focus in BYN was after I tried wiping the lens off and still had a bit of cloudiness.

 

can you be certain that the zoom in not dragging? Can you post one sub rather than a stacked image?

dj

https://i.imgur.com/ypdLpE2.jpg



#8 happylimpet

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Posted 14 September 2018 - 03:39 PM

Out of focus. Nothing to do with any fog on the lens.


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#9 fender2547886

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Posted 17 September 2018 - 09:31 AM

thanks for posting the single image. It looks like you are out of focus.



#10 mherbik

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Posted 17 September 2018 - 07:06 PM

No experience with camera lenses. If this was through a scope I would think something is off. At the very bottom center of image there is a star that looks closer to focus than the rest. It appears like there is severe coma when I look at the rest of the image. Again look at the bottom of image. Stars in center while out of focus are round and to either side the issues become wosre as you get father from center. I wouldn't pretend to know but Im sure dslr lenses have coma issues.




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